Glass-ceramics had their genesis in the U.S. Pat. No. 2,920,971. As is explained therein, the production of such articles contemplates three basic elements: (1) a glass-forming batch, customarily containing a nucleating agent, is melted; (2) the melt is simultaneously cooled to a temperature below the transformation range thereof and shaped into a glass body of a desired configuration; and (3) the glass body is exposed to a particularly-defined heat treatment which causes the growth of crystals in situ whereby the glass is converted into a predominantly and, frequently, virtually totally crystalline article.
The transformation range is generally considered to be that temperature at which a liquid melt has been transformed into an amorphous solid, that temperature commonly being deemed to reside in the vicinity of the annealing point of the glass. Where desired, as, for example, to visually inspect the glass quality of the precursor glass body, the glass melt may be cooled all the way to room temperature. Nevertheless, in the interests of production speed and energy economy, the commercial fabrication of glass-ceramics normally involves cooling the initial melt to only slightly below the transformation range and thereafter proceeding with the customary crystallization heat treatment. Frequently, the heat treatment is carried out in two steps: first, a nucleation step wherein the glass body is heated to a temperature within or somewhat above the transformation range and held for a sufficient length of time at that temperature to promote the development of nuclei and to initiate crystallization; and thereafter, second, a crystallization step wherein the nucleated body is heated to a higher temperature which at least approaches, and often exceeds, the softening point of the glass, and maintained for a sufficient length of time at that temperature to cause the growth of crystals on the nuclei.
Because of the normally highly crystalline microstructure existing in glass-ceramics, the physical properties demonstrated by such articles more nearly reflect the properties of the crystal phases present therein than the characteristics of the parent glass body. Moreover, inasmuch as the components of the crystal phase have been removed from the initial glass composition, the physical properties of whatever residual glass is left in the glass-ceramic will be quite different from those of the precursor glass. Furthermore, because crystallization is generated in situ, a glass-ceramic body manifests a geometry similar to the parent glass body and is free from voids and non-porous.
For further discussion of the preparation and qualities of glass-ceramics and the mechanism of crystal growth, reference is specifically made to U.S. Pat. No. 2,920,971.
Transparent glass-ceramic articles are known to the art. In general, the articles have displayed transparency because the crystals exhibited refractive indices very closely approximating that of the residual glass and/or demonstrated very low birefringence and/or the dimensions of the crystals were smaller than the wavelength of visible light. Examples of disclosures relating to the preparation of transparent glass-ceramics include:
U.S. Pat. No. 3,157,522 describes transparent glass-ceramics consisting essentially, in weight percent on the oxide basis, of
______________________________________ SiO.sub.2 55-75 Al.sub.2 O.sub.3 12-36 Li.sub.2 O 2-15 TiO.sub.2 3-7 ______________________________________
wherein the weight ratio Li.sub.2 O:Al.sub.2 O.sub.3 ranges between 0.1-0.6 and SiO.sub.2 +Al.sub.2 O.sub.3 +Li.sub.2 O+TiO.sub.2 is at least 95%.
The crystal phase consisted of beta-eucryptite and/or beta-spodumene and the coefficients of thermal expansion are stated to be less than 10.times.10.sup.-7 /.degree.C. (The coefficients of thermal expansion of the working examples ranged from -9.8 to 8.7.times.10.sup.-7 /.degree.C.)
U.S. Pat. No. 3,241,985 is concerned with transparent glass-ceramics consisting essentially, in weight percent on the oxide basis, of
______________________________________ SiO.sub.2 65-75 ZrO.sub.2 2-5 Al.sub.2 O.sub.3 12-27 TiO.sub.2 0-1.8 Li.sub.2 O 1.7-4.5 ______________________________________
wherein SiO.sub.2 +Al.sub.2 O.sub.3 +Li.sub.2 O&gt;85.
No identification of the crystal phase present is provided and the coefficients of thermal expansion of the working examples ranged from -3 to 14.times.10.sup.-7 /.degree.C.
U.S. Pat. No. 3,282,712 is directed to transparent glass-ceramics consisting essentially, in weight percent on the oxide basis, of
______________________________________ ZrO.sub.2 1-4 SiO.sub.2 55-70 TiO.sub.2 1-3 Al.sub.2 O.sub.3 20-35 P.sub.2 O.sub.5 1-5 Li.sub.2 O 3-5 ______________________________________
wherein ZrO.sub.2 +TiO.sub.2 +P.sub.2 O.sub.5 +SiO.sub.2 +Al.sub.2 O.sub.3 +Li.sub.2 O is at least 95.
Beta-eucryptite was observed to be the predominant crystal phase and the coefficients of thermal expansion of the working examples ranged from -5 to -10.times.10.sup.-7 /.degree.C.
U.S. Pat. No. 3,484,327 is drawn to transparent glass-ceramics consisting essentially, in weight percent on the oxide basis, of
______________________________________ SiO.sub.2 57-68 TiO.sub.2 0-6 Al.sub.2 O.sub.3 18-27 ZrO.sub.2 0-3 Li.sub.2 O 3.4-4.5 MgO 0-3 CaO 0-3 Na.sub.2 O 0-1 ZnO 0-2 P.sub.2 O.sub.5 0-3 B.sub.2 O.sub.3 0-4 ______________________________________
wherein
______________________________________ SiO.sub.2 + Al.sub.2 O.sub.3 &lt;82 SiO.sub.2 + Al.sub.2 O.sub.3 + B.sub.2 O.sub.3 + P.sub.2 O.sub.5 86-91 CaO + MgO + ZnO + Na.sub.2 O 2.5-6 SiO.sub.2 + Al.sub.2 O.sub.3 + P.sub.2 O.sub.5 + Li.sub.2 O &gt;93 TiO.sub.2 + ZrO.sub.2 2-6 ______________________________________
Beta-eucryptite and/or beta-spodumene comprises the predominant crystal phase and the coefficient of thermal expansion is observed to range from -10 to 10.times.10.sup.-7 /.degree.C.
U.S. Pat. No. 3,499,773 discloses transparent glass-ceramics consisting essentially, in weight percent on the oxide basis, of
______________________________________ SiO.sub.2 50-75 TiO.sub.2 0-6 Al.sub.2 O.sub.3 16-35 ZrO.sub.2 0-12 Li.sub.2 O 2.5-6 SnO.sub.2 0-12 ______________________________________
wherein TiO.sub.2 +ZrO.sub.2 +SnO.sub.2 1.5-12.
Beta-eucryptite constitutes the predominant crystal phase and the coefficient of thermal expansion is stated to range from -12 to 12.times.10.sup.-7 /.degree.C.
U.S. Pat. No. 3,625,718 discusses transparent glass-ceramics consisting essentially, in weight percent on the oxide basis, of
______________________________________ SiO.sub.2 64-74 TiO.sub.2 1.2-2.4 Al.sub.2 O.sub.3 15-23 ZrO.sub.2 0-2 Li.sub.2 O 3.3-4.8 MgO 0-2.5 ZnO 1-3.8 CaO 0-2.5 ______________________________________
Beta-eucryptite comprises the predominant crystal phase and the coefficients of thermal expansion of the working examples range from -13 to 0.4.times.10.sup.-7 /.degree.C.
U.S. Pat. No. 3,677,785 describes transparent glass-ceramics consisting essentially, in weight percent on the oxide basis, of
______________________________________ SiO.sub.2 65-75 MgO 1.3-2 Al.sub.2 O.sub.3 15-25 BaO + MgO 2.6-5 Li.sub.2 O 2.5-4.5 ZrO.sub.2 1-2 BaO 1.3-4 TiO.sub.2 1-2 ______________________________________
The crystal phase is not identified and the coefficients of thermal expansion of the working examples range from -6 to 13.times.10.sup.-7 /.degree.C.
U.S. Pat. No. 3,788,865 is concerned with transparent glass-ceramics consisting essentially, in weight percent on the oxide basis, of
______________________________________ SiO.sub.2 50-75 F.sub.2 0-0.2 Al.sub.2 O.sub.3 16-35 Alkaline Earth Oxides 0-4.5 Li.sub.2 O 3-5.5 ZnO 0-4 B.sub.2 O.sub.3 0-9 Na.sub.2 O 0-2 ZrO.sub.2 0-5 Colorant 0.005-2 TiO.sub.2 0-10 ZrO.sub.2 + TiO.sub.2 + SnO.sub.2 Not Over 10 SnO.sub.2 0-5 SiO.sub.2 + Al.sub.2 O.sub.3 75-92 P.sub.2 O.sub.5 0-3 ______________________________________
Beta-eucryptite and/or beta-spondumene comprises the predominant crystal phase and the coefficient of thermal expansion is observed to range from -10 to 10.times.10.sup.-7 /.degree.C.
U.S. Pat. No. 3,928,229 is drawn to transparent glass-ceramics consisting essentially, in weight percent on the oxide basis, of
______________________________________ SiO.sub.2 50-70 TiO.sub.2 1-3 P.sub.2 O.sub.5 0-10 ZrO.sub.2 1-3 Al.sub.2 O.sub.3 15-30 As.sub.2 O.sub.3 0-2 Li.sub.2 O 2-8 Sb.sub.2 O.sub.3 0-2 Na.sub.2 O 0.2-2 Nd.sub.2 O.sub.3 1-8 MgO 0-3 MgO + CaO 0.5-3 CaO 0-3 As.sub.2 O.sub.3 + Sb.sub.2 O.sub.3 0-2 ZnO 0.5-3 ______________________________________
The crystal phase is not identified and the coefficient of thermal expansion is noted as ranging from 0.2-5.times.10.sup.-7 /.degree.C.
U.S. Pat. No. 4,018,612 is directed to transparent glass-ceramics consisting essentially, in weight percent on the oxide basis, of
______________________________________ Li.sub.2 O 2.5-3.5 SiO.sub.2 67-70 MgO 1.5-2.5 TiO.sub.2 2-4.5 ZnO 1-2 ZrO.sub.2 1-2 Al.sub.2 O.sub.3 17.75-20 BaO 0-2 ______________________________________
Beta-quartz solid solution constitutes the predominant crystal phase and the coefficients of thermal expansion of the working examples range from 6.8-10.times.10.sup.-7 /.degree.C.
U.S. Pat. No. 4,093,468 relates to transparent glass-ceramics consisting essentially, in weight percent on the oxide basis, of
______________________________________ SiO.sub.2 60-70 TiO.sub.2 0.5-6 Al.sub.2 O.sub.3 15-25 Nd.sub.2 O.sub.3 0.03-0.75 Li.sub.2 O 3-4 Fe.sub.2 O.sub.3 Up to 0.05 ______________________________________
Beta-quartz solid solution is said to comprise the predominant crystal phase and the coefficient of thermal expansion is stated to be less than 15.times.10.sup.-7 /.degree.C.
U.S. Pat. No. 4,192,688 refers to transparent glass-ceramics consisting essentially, in weight percent on the oxide basis, of
______________________________________ SiO.sub.2 50-75 B.sub.2 O.sub.3 0-9 Al.sub.2 O.sub.3 16-35 P.sub.2 O.sub.5 0-3 SiO.sub.2 + Al.sub.2 O.sub.3 75-92 F.sub.2 0-0.2 Li.sub.2 O 3-5.5 RO 0-4.5 ZrO.sub.2 0-5 ZnO 0-4 TiO.sub.2 0-10 Na.sub.2 O 0-2 SnO.sub.2 0-5 CaO + NiO 0.005-2 ZrO.sub.2 + TiO.sub.2 + SnO.sub.2 2-10 ______________________________________
Beta-eucryptite and/or beta-spodumene constitutes the predominant crystal phase and the coefficient of thermal expansion is noted as ranging between -12 to 10.times.10.sup.-7 /.degree.C.
U.S. Pat. No. 4,285,728 discloses transparent glass-ceramics consisting essentially, in weight percent on the oxide basis, of
______________________________________ SiO.sub.2 56-70 MgO 0-3 Al.sub.2 O.sub.3 18-27 Na.sub.2 O 0-1 Li.sub.2 O 3.4-4.5 P.sub.2 O.sub.5 0-3 CaO 0-3 SiO.sub.2 + Al.sub.2 O.sub.3 At least 82 ZnO 0-2 SiO.sub.2 + Al.sub.2 O.sub.3 + B.sub.2 O.sub.3 + P.sub.2 O.sub.5 86-91 B.sub.2 O.sub.3 0-4 CaO + MgO + ZnO + Na.sub.2 O 2.5-6 TiO.sub.2 0-6 SiO.sub.2 + Al.sub.2 O.sub.3 + P.sub.2 O.sub.5 + Li.sub.2 Not More Than 93 ZrO.sub.2 0-3 TiO.sub.2 + ZrO.sub.2 2-6 ______________________________________
Beta-eucryptite and/or beta-spodumene comprises the predominant crystal phase and the coefficient of thermal expansion is asserted to range between -10 to 10.times.10.sup.-7 /.degree.C.
The decoration of ceramic articles through the application of glazes has been practiced for millenia. In addition to enhancing aesthetics, however, glazes have also been employed to improve the resistance of the product from attack by comestibles and other chemical agents, and glazes have been developed having a lower coefficient of thermal expansion than that of the article to be coated such that, when the glaze is cooled to room temperature after its application, it will form a compressive surface layer on the article, thereby increasing the overall mechanical strength of the article.
Glazes have been applied to glass-ceramic articles; e.g., dinnerware marketed by Corning Glass Works, Corning, N.Y., under the trademark CENTURA.RTM.. Those articles consisted of a body of glass-ceramic having an average coefficient of thermal expansion (0.degree.-300.degree. C.) of about 81.times.10.sup.-7 /.degree.C. and a vitreous glaze exhibiting a lower coefficient of thermal expansion. The surface compression layer provided by the glaze yielded a composite body demonstrating a mechanical strength in excess of two times that of the glass-ceramic alone.
There has been the desire to develop glazes having negative coefficients of thermal expansion for application to glass, glass-ceramic, and ceramic articles having a very low or zero coefficient of thermal expansion. For example, opaque glass-ceramic culinary ware is marketed by Corning Glass Works as Code 9608 and under the trademark CORNING WARE.RTM., that glass-ceramic exhibiting an average coefficient of thermal expansion (0.degree.-300.degree. C.) of about 12.times.10.sup.-7 /.degree.C. Also, opaque glass-ceramic sheet for use as cooking surfaces and counter tops is marketed by Corning Glass Works as Code 9617, that glass-ceramic displaying an average coefficient of thermal expansion (0.degree.-300.degree. C.) of about 9.times.10.sup.-7 /.degree.C. Those products have the approximate analyses tabulated below in weight percent:
______________________________________ 9608 9617 ______________________________________ SiO.sub.2 69.5 66.7 Al.sub.2 O.sub.3 17.6 20.5 Li.sub.2 O 2.7 3.5 MgO 2.6 1.6 ZnO 1.0 1.2 TiO.sub.2 4.7 4.8 ZrO.sub.2 0.2 0.05 As.sub.2 O.sub.3 0.9 0.4 F 0.03 0.22 Fe.sub.2 O.sub.3 0.06 0.035 B.sub.2 O.sub.3 0.07 MnO.sub.2 0.03 ______________________________________
In Code 9608 and 9617 products the predominant crystal phase is beta-spodumene.
Therefore, one objective of considerable research has been to develop glazes having very low or negative expansion coefficients which, when applied to glass, glass-ceramic, and ceramic substrates exhibiting average coefficients of thermal expansion of less than 15.times.10.sup.-7 /.degree.C., will provide a durable, attractive, decorative surface compression layer thereon to significantly enhance the mechanical strength of the substrate.
Inasmuch as a very important utility for glazed bodies is in dinnerware applications where the use temperature customarily ranges between about 25.degree.-100.degree. C., one specific objective of the present invention is to produce chemically durable glazes which are compatible with low expansion dinnerware materials. The resulting surface compression layer yields a composite article demonstrating much more than twice the mechanical strength of the original body, plus it imparts an attractive appearance to the dinnerware coupled with excellent resistance to chemical attack.